The invention relates to voltage regulators. More particularly, the inventions described herein relate to systems and methods for interconnecting voltage regulators to provide simple current sharing techniques and improved regulation characteristics.
Voltage regulators are found in virtually every device that requires electricity. The purpose of a voltage regulator circuit is to control and regulate voltage from a power source to a load, typically through certain conditioning and regulation circuitry. A typical application of voltage regulator circuitry is to convert AC power, provided by a power utility, to a regulated DC voltage suitable for use with consumer electronics. Such power supplies are controlled by a voltage regulator. Although voltage regulators are implemented as stand alone systems, often they are constructed as integrated circuits (ICs) and used in various applications including communication and computing systems.
Two or more voltage regulators may be connected together to provide greater output current. Factors favoring the parallel of connection voltage regulators include the need to dissipate heat over a wider area as well as increase output current. In some instances, many voltage regulators may be connected together to provide additional voltage to a load. In other instances, the voltage regulators may be connected in parallel to provide additional load current. In such instances, the connected voltage regulators are typically configured in an attempt to share current to the load. This may be done in order to promote load balancing and/or to maintain system operation within a desired peak temperature range.
As manufactured, voltage regulators experience wide variation in output voltage, thereby making current matching between directly paralleled voltage regulators relatively difficult to achieve.
The portion of load current supplied by each parallel connected voltage regulator is often dependent on the difference in output voltage and output impedance of the respective voltage regulators. Thus, when voltage regulators are connected in parallel, the regulator having the higher output voltage typically supplies more current than the supply with a lower output voltage. As a result, the supply with the higher output voltage may provide most or all of the current to the load. Moreover, the regulator providing the highest output voltage may limit in overload before the other regulators begin to supply current. This unbalanced condition is further exacerbated if the regulator with the higher output voltage also has the lower output impedance of the two (or more) supplies.
The unequal sharing of load current by paralleled voltage regulators may degrade both the performance and reliability of a power system. This problem is of particular concern for surface mounted voltage regulators due to the inherent limitation of power dissipation when mounted on a circuit board. In certain situations, the additional thermal stress resulting from such severe current imbalances may reduce component lifetime in the sourcing supply by 50% or more.
Various techniques have been used to balance current among parallel connected voltage regulators. One known current sharing technique involves the use of a “share bus” configuration in which output current information is shared among the parallel connected regulators to regulate current. In such systems, a current sense resistor is used to develop a voltage which represents the output current of the parallel connected voltage regulators. This voltage is reproduced on the share bus and monitored by the voltage regulators to determine how much current to provide. Because the power supplies are providing current based on both an internal error voltage (for individual supply regulation) and the voltage on the share bus (for group regulation), current is supplied approximately equally. One drawback with this arrangement, however, is the need for complicated controller circuitry and specialized interconnections among the voltage regulators.
Accordingly, it would be desirable to provide circuits and methods for the efficient sharing of current among paralleled voltage regulators that does not degrade voltage regulation.
Moreover, it would be desirable to provide circuits and methods for heat dissipation in parallel coupled voltage regulators that result in improved current sharing.